I have a bone to pick with our so called illustrious channel providers.Why is it when you have set the volume on your tv to a comfortable level they up the volume on commercials ridiculously loud I know why ,they want to sell their product it seems car dealars are the worst.Two years ago I had to get a new tv and I swore I was going to buy one with a sound adjuster but I ended up getting a Sony Wega the deal was too good to pass up now I think I made a mistake as it doesn't have this feature.Seems the loudness on comercials is getting worse and worse.
Really irritating when you are trying to keep quiet watching a movie whilst hubby is trying to sleep

finally, a question right up my alley...
there are fcc regulations regarding audio and video levels for broadcast. there is a maximum allowable level, but most shows record within the legal limits, often a bit below the max to be sure.
commercial producers, however, record and transfer their shows to the broadcasters at the maximum level, often pushing or slightly topping the limits, for obvious reasons.
so when broadcast back to back, the commercials sound louder.
it's all just a matter of tweaking a few dB's, but no one actively rides the audio levels from commercial to program, and vice versa, so long as they're within or close to specs.

video levels are more closely watched because of their nature. go to high on your white level, and your speakers will buzz. go too hot on your chroma, and the picture will bleed or wash out. there's not as much leighway with video as there is with audio.

the digital world including high definition should eventually change all of that.

forget subliminal messages. that's too easy.
did you know that a provider can imperceptibly speed up a show, and be able to slip in an extra commercial or two? it's illegal, but it's done.

something i was working on tonight was encoding a signal into the vertical interval preventing tivo like devices from recording "the masters" highlights on other-than-cbs broadcasts.

What bugs me most is the canned laughter on sit-coms. If you're in the next room (or away from the TV while they're on) the laugh track is the only part of the show you can hear... Do we really have to be told when to laugh? Is the writing that weak? Are we such sheep that we are only able to laugh ALONG?